Normative: add Iterator.zip and Iterator.zipKeyed

[michaelficarra]

Pending Stage 4 for https://github.com/tc39/proposal-joint-iteration. Fixes tc39/proposal-joint-iteration#48.

[github-actions]

The rendered spec preview for this PR is available as a single page at https://tc39.es/ecma262/pr/3802 and as multiple pages at https://tc39.es/ecma262/pr/3802/multipage .

[gibson042]

It's a bit odd to read padding only when mode is "longest" (rather than unconditionally), but it was present from the start and is covered in test262. I'm not objecting, but do want to draw attention to this behavior.

[jmdyck]

Suggested change

	<p>This method performs the following steps when called:</p>
	<p>This function performs the following steps when called:</p>

... because it's not a property of a prototype and doesn't reference *this*? (There's nothing in Editorial Conventions to say.)

[michaelficarra]

We could add an editorial convention for this if we can come up with a good rule.

[jmdyck]

For some earlier discussion, see issue #2576.

[jmdyck]

Oh, I forgot to mention: it's unusual to have the section for an AO (in this case IteratorZip) appear as a child of a "Properties of the X" section.

[michaelficarra]

Oh, I forgot to mention: it's unusual to have the section for an AO (in this case IteratorZip) appear as a child of a "Properties of the X" section.

This seems like the most appropriate place, though. Where would you put it?

[jmdyck]

This seems like the most appropriate place, though. Where would you put it?

Precedent elsewhere in the spec would suggest nesting it within the section for Iterator.zip or Iterator.zipKeyed.

E.g.,

• The AO ObjectDefineProperties is invoked by functions Object.create and Object.defineProperties, and is nested within the latter.
• The AO ThisBooleanValue is invoked by Boolean.prototype.toString and Boolean.prototype.valueOf, and is nested within the latter.
• The AO ThisSymbolValue is invoked by Symbol.prototype.valueOf and Symbol.prototype [ %Symbol.toPrimitive% ], and is nested within the former.
• Similarly with GetOwnPropertyKeys, ThisNumberValue, ThisBigIntValue, StringPaddingBuiltinsImpl, GetSubstitution, TrimString, ThisStringValue, etc.

Alternatively, the spec sometimes puts AOs in an "Abstract Operations for Foo" section after the "Properties of Foo" section.

[gibson042]

Alternatively, the spec sometimes puts AOs in an "Abstract Operations for Foo" section after the "Properties of Foo" section.

I like this approach.